The invention relates to an exterior electrical box for use in particular on ships. A corrosion resistant bimetallic mounting flange and electrical box and the method of making the same by explosive bonding is disclosed.
In the topside environment of sea going vessels extreme seawater induced corrosion problems exist. Moreover, if the metals used for construction of ship parts are galvanically dissimilar and/or if there are crevices between metal components, the corrosion problems are aggravated.
Corrosion problems are especially recurrent in shipboard electrical boxes as where maintenance requirements necessitate that the box covers be periodically removed, creating crevice problems in and around the box covers. Most of the general corrosion problems on a ship and the crevice caused corrosion around electrical box covers can be eliminated through the use of corrosion resistant materials, such as brass or MONEL for the box and cover.
Brass and MONEL however are difficult to use as they present attachment problems. On ships the common bulkhead materials are aluminum and steel. Since neither brass nor MONEL can be welded effectively to either the aluminum or steel, the boxes must be bolted to the ship's structure. Dissimilar metal and crevice corrosion is then created at the junction between a box and the bulkhead to which it is attached.
In shipboard electrical systems, electrical components frequently require EMI/EMP protection, and shielding is required of the wires and the points where the wires enter the electrical boxes. All the electrical components, including the shielded layers, must be electrically bonded. Corrosion between components in shipboard structures can interfere with electrical continuity, making it necessary to protect the components of the electrical system from corrosion so that the shielding and bonding mechanisms are not subject to environmental damage. All of these concerns are diminished if the electrical box containing the electrical components is recessed into the bulkhead structure. But on shipboard, particularly in the topside environment, electrical boxes are typically surface mounted and exposed to the sea environment. They cannot be recessed into the bulkheads because of the lack of weldability between the brass or aluminum box and the steel bulkhead structure.
In addition to the corrosion problems which are inherent with such a system, winter topside icing exacerbates the dilemma of surface mounted electrical boxes when the boxes are knocked off the walls by de-icing procedures.
Metallurgical bonding techniques such as explosion bonding have been used in the past to alleviate the corrosion concerns of a shipboard environment. U.S. Pat. No. 4,934,952 discloses the use of explosion bonded dissimilar metallic components for use in a corrosive environment. The patent, in particular, is directed to a corrosion resistant bonding strap.
U.S. Pat. No. 3,137,937 discloses a general process for explosion bonding of dissimilar metals.
It is therefore the primary object of the present invention to provide an electrical box in which the cover and the cover mounting flange are similar, non-corrosive metals which will avoid corrosion in the gap between the cover and the flange.
A second object of this invention is to provide a bimetallic flange for the electrical box which will serve the first object and at the same time provide a second metal which is weldable to the structure to which the electrical box will be attached and which will present no gap or crevice between the two dissimilar metals which will foster galvanic corrosion.